1. Field of the Invention
The present invention relates to a method of forming miniature wiring and connector systems for electrical products. More specifically the present invention relates to a method of forming electrode arrays, such as arrays for sensors, including biosensors, and implantable devices, such as an implantable recording or stimulating electrode or pad for use in the body. An electrode array formed using the method is also described.
2. Related Art
In many electrical devices, particularly those that are manufactured on a very small scale, the manufacture of the wiring and connector components is often a labour intensive and specialised craft. Ensuring that the wiring and connection of the various components of the systems occurs correctly is often the most expensive and labour intensive aspect of the manufacturing process, resulting in large costs associated with the time taken to manufacture the device which is often passed on to the ultimate consumer. This is also the case when such devices need to be specifically hand made to a specification as often the availability of the device is dependant upon the time taken to manufacture the device, with the time taken being difficult or impossible to expedite.
This is particularly the case in the field of medical implants and electrical devices that are implanted in the body to perform a specific task. Such devices may include: stimulating devices such as pacemakers, cochlear implants, FES stimulators; recording devices such as neural activity sensors and the like; implantable cables which may be used to connect implantable devices to other implantable devices or stimulating/sensing devices; diagnostic devices capable of carrying out in-vivo analysis of body parameters; and other types of implantable devices not yet contemplated. In such devices, the size needs to be minimised to ensure that they are minimally invasive upon implantation. As a result, in such instances, the electronic wiring and connections need also to be relatively very small. As such, manufacturing such devices to ensure that they are reliable and sturdy is a specialised art, and requires much time and expense.
As a result of the need to increase the miniaturisation of such devices, a wide range of techniques have been developed to create patterned components which would be too difficult or impossible to create by hand design and satisfy the high volume supply required. Techniques such as electroforming, vacuum deposition (sputtering, evaporation), and chemical vapour deposition, to name a few, are some of the known ways to produce patterned electrically conductive features on insulating surfaces on a micron scale. The problem with such methods however, has been that the metallic films produced by these techniques have been shown to feature properties that are different from the corresponding properties of the bulk materials used. This results in the desired materials functioning differently from their intended purpose, and in the particular case of platinum, the thin films have tended to crack and exhibit large impedance as well as a high degree of delamination.
In the manufacture of such devices, the bulk material is chosen based on the properties it exhibits. In the case of implantable electrical components, platinum has been found to exhibit particularly useful properties for such an application, namely good conductivity and inertness. With this being understood, it is beneficial in the manufacture of such devices for the bulk material to exhibit the same properties, especially physical properties, after manufacture as it did prior to manufacture, as discussed above. Variations in these properties can have a bearing on the functionality of the device, which, particularly in medical implanted devices, is highly undesirable. As mentioned, platinum films tend to crack and delaminate, hence delivering high impedance which impairs the functionality of the device. The use of thin film technology has been shown to work for a number of materials such as copper, gold and nickel, however none of these materials are suitable for active implantable devices.
Other more conventional methods of manufacturing such devices would be to directly stamp the desired components out of a conductive sheet using a fine blanking or stamping method. This is possible for applications whereby single components having large dimensions are stamped and the components do not need to be thin and flexible. However, simple stamping techniques are not suitable for multiple components having very small dimensions made out of thin conductive sheets, such as those proposed to be covered by the present invention. In such applications, the line width dimensions of the components and between the components are too small for stamping machines and the sheet material is too thin to provide the precision required for such components.
Because of these problems, medical implants, such as cochlear implants, are still manufactured using labour intensive manual procedures.
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Of these types, conductive hearing loss occurs where the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss may often be helped by use of conventional hearing aids, which amplify sound so that acoustic information does reach the cochlea and the hair cells.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to or absence of the mechanism for nerve impulses to be generated from sound in the normal manner.
It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. U.S. Pat. No. 4,532,930, the contents of which are incorporated herein by reference, provides a description of one type of traditional cochlear implant system.
Typically, cochlear implant systems have consisted of essentially two components, an external component commonly referred to as a processor unit and an internal implanted component commonly referred to as a receiver/stimulator unit. Traditionally, both of these components have cooperated together to provide the sound sensation to a user.
The external component has traditionally consisted of a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts speech into a coded signal, a power source such as a battery, and an external transmitter coil.
The coded signal output by the sound processor is transmitted transcutaneously to the implanted receiver/stimulator unit situated within a recess of the temporal bone of the user. This transcutaneous transmission occurs via the external transmitter coil that is positioned to communicate with an implanted receiver coil provided with the receiver/stimulator unit. This communication serves two essential purposes, firstly to transcutaneously transmit the coded sound signal and secondly to provide power to the implanted receiver/stimulator unit. Conventionally, this link has been in the form of a radio frequency (RF) link, but other such links have been proposed and implemented with varying degrees of success.
The implanted receiver/stimulator unit traditionally includes a receiver coil that receives the coded signal and power from the external processor component, and a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlea electrode assembly which applies the electrical stimulation directly to the auditory nerve producing a hearing sensation corresponding to the original detected sound.
It is known in the art that the cochlea is tonotopically mapped. In other words, the cochlea can be partitioned into regions, with each region being responsive to signals in a particular frequency range. This property of the cochlea is exploited by providing the electrode assembly with an array of electrodes or stimulating pads, each electrode or pad being arranged and constructed to deliver a stimulating signal within a preselected frequency range to the appropriate cochlea region. The electrical currents and electric fields from each electrode or pad stimulate the nerves disposed on the modiolus of the cochlea. As the size of the cochlea is very small and the electrode assembly needs to be flexible enough to be inserted into the cochlea, the dimensions of the electrode assembly are such that do not allow for traditional manufacturing techniques.
For this reason, the intracochlear electrode array has generally been formed in a manual process by positioning a plurality (eg. 22) of electrically conductive platinum rings in a linear array and then welding electrical conductive wires to each of the electrodes or pads. This process can lead to small variations in the locations of the electrodes or pads and wiring from one manufactured array to the next with consequent small variations in the overall mechanical properties of the array once a resiliently flexible carrier member is moulded about the array. Each of the wires require connection to the receiver/stimulator unit and in order to ensure system integrity, each of the wires have been insulated from the others so that unwanted interaction between different electrical components is eliminated.
While the above method has proven very successful, it is labour intensive and hence a relatively expensive process. With implanted devices and miniaturisation becoming more common, there is an increasing need to provide electronic wiring and electronic connections in such systems that are both simple and reliable. The present invention is directed to a new method of forming such wiring and connections that addresses at least some of the problems with prior art processes.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.